Remarkably high hydration capability of BaSn1–xInxO3–δ perovskite materials: What do we need to know about protons in complex oxides?

Abstract

Proton-conducting oxides constitute a wide class of materials that exhibit pronounced proton transport in humid atmospheres. Owing to their high proton mobility, these oxides are regarded as promising electrolytes for low- and intermediate-temperature protonic ceramic fuel cells and electrolysis cells, which offer efficient and clean energy conversion. Protons appear in complex oxides through a dissociative water adsorption process, which consists of the interaction between existing oxygen vacancies and water molecules in the gas phase. This process is also known as hydration or water uptake. Within the present work, we analyze the hydration features of BaSn_1–xIn_xO_3–δ perovskite materials (BSIx), which include a wide range of solid solutions (0 ≤ x < 0.7) and a nearly theoretical hydration limit for almost all studied compounds at the same time. The latter is a unique property of In-doped stannates, which is untypical for most other proton-conducting oxides. Along with the experimental data on the water uptake of BSIx, we provide an in-depth investigation of proton concentrations depending on external factors, involving a further comparison with literature data on materials hydration, as well as the discovery of hidden relationships between proton concentration and various functional properties. Therefore, this work contributes to theoretical and applied investigations of proton-conducting oxides, especially in the context of their hydration behavior.